$_FILES Array getting empty when using $this->form_validation->run()

If I use both in same query how I can get the last inserted id from 

PHP Code:

$my_result = $this->My_Backend_Model->lets_insert_form_post($data); 


To insert image I need the last inserted id return from the above query. Then only I can do

PHP Code:

$my_result = $this->My_Backend_Model->lets_upload_photo($data2); 


Because

PHP Code:

$data2 = array('path'=>$imagePath,'propertyid'=>$propertyid); 


Here I want to pass the id as propertyid returned from the first query. How I can use then if we use the both operations in same variable ?